Multiple channel, sequential, cardiac pacing systems

ABSTRACT

Multi-chamber cardiac pacing systems for providing synchronous pacing to at least the two upper heart chambers or the two lower heart chambers or to three heart chambers or to all four heart chambers employing programmable conduction delay window (CDW) times timed out from paced and sensed events occurring in each heart chamber are disclosed. The synchronous pacing of one of the right and left heart chambers is provided on demand following expiration of programmable pace and sense CDWs that are started by both a paced event and a sensed event first occurring in the other of the right and left heart chambers. The delivery of the pacing pulse is inhibited by a sensed event detected in the other of the right and left heart chambers before the expiration of the corresponding CDW. In a four channel atrial and ventricular pacing system, the right and left atrial chambers are sensed and paced as necessary upon at the end of a V-A escape interval and right and left AV delays are commenced for sensing ventricular depolarizations in the right and left ventricles. The four channel system is programmable to pace and sense in three selected heart chambers.

This application is a divisional application of U.S. patent applicationSer. No. 09/067,729 filed Apr. 28, 1998 entitled "Multiple Channel,Sequential, Cardiac Pacing Systems" to Struble et al.

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is hereby made to commonly assigned U.S. Pat. No. 5,902,324filed on even date herewith for BI-ATRIAL AND/OR BI-VENTRICULAR,SEQUENTIAL CARDIAC PACING SYSTEMS filed in the names of D. Thompson etal.

FIELD OF THE INVENTION

The present invention pertains to multi-chamber cardiac pacing systemsfor providing synchronous pacing to at least the two upper heartchambers or the two lower heart chambers or to three heart chambers orto all four heart chambers employing programmable conduction delaywindow (CDW) times timed out from paced and sensed events occurring ineach heart chamber.

BACKGROUND OF THE INVENTION

The cardiovascular system provides oxygenated blood to variousstructures of the body. In a normally functioning heart, the body'sdemand for oxygenated blood varies, and the heart responds by increasingor decreasing its rate and force of contraction to meet the demand. Anelectrical signal generated by the sinus node in the upper right atrialwall near the base of the heart is conducted through the upper heartchambers, i.e., the right and left atria, and causes them to contract ina synchronous manner. The contraction of the upper heart chambers forcesblood pooled therein through open heart valves and into the right andleft ventricles or lower heart chambers. The atrial electricaldepolarization wave arrives at the AV node superior to the ventriclesand triggers the conduction of a ventricular depolarization wave downthe bundle of His in the septum between the right and left ventricles tothe apex of the heart. The ventricles contract after a briefatrio-ventricular (AV) delay time following the sinus nodedepolarization as the depolarization wave then advances superiorly,posteriorly, and anteriorly throughout the outer ventricular wall of theheart. The lower heart chambers contract and force the blood through thevascular system of the body. The contraction of the right and leftventricles proceeds in an organized fashion which optimizes emptying ofthe ventricular chambers. The synchronous electrical depolarization ofthe atrial and ventricular chambers can be electrically sensed anddisplayed, and the electrical waveform is characterized by acceptedconvention as the "PQRST" complex. The PQRST complex includes theP-wave, corresponding to the atrial depolarization wave, the R-wave,corresponding to the ventricular depolarization wave, and the T-wavewhich represents the re-polarization of the cardiac cells.

Various disease mechanisms cause conduction disturbances which interferewith the natural conduction system of the heart and affect the heart'sability to provide adequate cardiac output to the body. In certaindisease mechanisms, the sinus node fails to depolarize and commence theP-wave as rapidly as required to satisfy the demand for oxygenatedblood, or the atria may spontaneously depolarize at rates that are wellin excess of the ability of the ventricles to respond. In thesesituations, the ventricles may compensate by depolarizing spontaneouslyfrom ectopic depolarization sites. In other cases where the SA nodeoperates correctly, 1:1 atrial and ventricular depolarization synchronyis lost because the AV node fails to respond to all P-waves or a defectin the bundle of His interferes with the conduction of the ventriculardepolarization. In all of these cases, the ventricles may contract at aninadequate rate to provide adequate cardiac output.

When the atria or ventricles contract too slowly, the patient may be acandidate for implantation with a cardiac pacemaker for restoring theheart rate by applying pacing pulses to the heart chamber that ismalfunctioning at a pacing rate that restores adequate cardiac output.Modem implantable cardiac pacemakers comprise an implantable pulsegenerator (IPG) and a lead or leads extending from the IPG to pace/senseelectrode or electrodes located with respect to the heart chamber todeliver the pacing pulses and sense the P-wave or R-wave. Typically, theleads are transvenously introduced into the particular heart chamber viathe superior vena cava and right atrium, and the pace/sense electrodesare maintained in contact with the heart tissue by a fixation mechanismat the distal end of the lead. However, leads may be placedsubcutaneously between the IPG and the exterior of the heart, and thepace/sense electrodes attached to the epicardium at the desired sites.Moreover, endocardial coronary sinus leads are introduced through theright atrium into the coronary sinus and the great vein to locatepace/sense electrodes in proximity to the left atrium or the leftventricle.

A single chamber, demand pacemaker is implanted to supply pacing pulsesto a single upper or lower heart chamber, typically the right atrium orright ventricle, in response to bradycardia of the same chamber. In anatrial, demand pacemaker operating in the AAI pacing mode, an atrialpacing pulse is delivered to the atrial pace/sense electrodes by the IPGif a P-wave is not sensed by an atrial sense amplifier coupled to theatrial pace/sense electrodes within an atrial escape interval (A--Ainterval) timed by an atrial escape interval timer. In a ventricular,demand pacemaker operating in the VVI pacing mode, a ventricular pacingpulse to the ventricular pace/sense electrodes if an R-wave is notsensed by a ventricular sense amplifier coupled to the ventricularpace/sense electrodes within a ventricular escape interval (V--Vinterval) timed by a ventricular escape interval timer.

A dual chamber, demand pacemaker is implanted to supply pacing pulseswhen required to one upper heart chamber and to one lower heart chamber,typically the right atrium and right ventricle. In a dual chamber,demand pacemaker operating in the DDD pacing mode, both the AAI and VVIpacing modes are followed under the above defined conditions. Aventricular pacing pulse is delivered to the ventricular pace/senseelectrodes if an R-wave is not sensed by the ventricular sense amplifiercoupled thereto within an AV time interval timed from the sensing of aP-wave by the atrial sense amplifier.

Over the years, it has been proposed that various conductiondisturbances involving both bradycardia and tachycardia of a heartchamber could benefit from stimulation applied at multiple electrodesites positioned in or about it in synchrony with a depolarization whichhas been sensed at least one of the electrode sites. In addition, it hasbeen proposed to employ pacing to compensate for conduction defects andin congestive heart failure where depolarizations that naturally occurin one upper or lower chamber are not conducted quickly enough to theother upper or lower heart chamber. In such cases, the right and leftheart chambers do not contract in optimum synchrony with each other, andcardiac output suffers due to the timing imbalance. In other cases,spontaneous depolarizations of the left atrium or left ventricle occurat ectopic foci in these left heart chambers, and the natural activationsequence is grossly disturbed. In such cases, cardiac outputdeteriorates because the contractions of the right and left heartchambers are not synchronized sufficiently to eject blood therefrom.

In patients suffering from congestive heart failure, the hearts becomedilated, and the conduction and depolarization sequences of the heartchambers may exhibit Intra-Atrial Conduction Defects (IACD), Left BundleBranch Block (LBBB), Right Bundle Branch Block (RBBB), and IntraVentricular Conduction Defects (IVCD). Single and dual chamber pacing ofthe right atrium and/or right ventricle can be counterproductive in suchcases, depending on the defective conduction pathway and the locationsof the pace/sense electrodes.

A number of proposals have been advanced for providing pacing therapiesto alleviate these conditions and restore synchronous depolarization ofright and left, upper and lower, heart chambers. The proposals appearingin U.S. Pat. Nos. 3,937,266, 4,088,140, 4,548,203, 4,458,677, 4,332,259are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259, allincorporated herein by reference. The advantages of providing sensing atpace/sense electrodes located in both the right and left heart chambersis addressed in the '688 and '259 patents, as well as in U.S. Pat. Nos.4,354,497, 5,174,289, 5,267,560, 5,514,161, and 5,584,867, alsoincorporated herein by reference. Typically, the right atrium is pacedat expiration of an A-A escape interval, and the left atrium issimultaneously paced or synchronously paced after a short delay time.Similarly, the right ventricle is paced at expiration of a V-V escapeinterval, and the left ventricle is simultaneously paced orsynchronously paced after a short delay time. Some of these patentspropose limited forms of DDD pacing having "bi-ventricular" or"bi-atrial" demand or triggered pacing functions. In all cases, a pacingpulse delivered at the end of an escape interval or at the end of an AVdelay (a "paced event") triggers the simultaneous or slightly delayeddelivery of the pacing pulse to the other heart chamber. They do notpropose pacing a right or left heart chamber at the end of the escapeinterval or AV delay and then inhibiting pacing in the other of theright or left heart chamber if a conducted depolarization is detected inthat other heart chamber within a physiologic time related to thelocation of the pace/sense electrodes.

In the above-incorporated '259 patent, a combined epicardial IPG andelectrode array are proposed for fitting about the apical region of theheart and providing a VVI pacing function providing for substantiallysimultaneous depolarization of both ventricles through selected ones ofthe pace/sense electrodes on time out of a V--V escape interval. It isnot clear what occurs if an R-wave is sensed at one of the left or rightventricular pace/sense electrodes within the V--V escape interval.

In the '688 patent, two or three chamber pacing systems are disclosedwherein a programmable synchronization time window of about 5-10 msecduration is started on sensing an R-wave or a P-wave at pace/senseelectrodes in one of the ventricles or atria before the expiration of aV--V or an A--A escape interval, respectively. The delivery of thepacing pulse in the other atrium or ventricle is inhibited if a P-waveor an R-wave is sensed at the pace/sense electrode site in that chamberwithin the synchronization time window. Atrial or ventricular pacingpulses are delivered simultaneously to both left and right atrial orventricular pace/sense electrodes, if the V--V escape interval times outwithout sensing a P-wave or an R-wave at either pace/sense electrodesite. In a DDD pacemaker context, an atrial pace/sense electrode, senseamplifier and pace output circuit and a pair of ventricular pace/senseelectrodes, sense amplifiers and pace output circuits are provided. TheAV delay timer is started when a P-wave is sensed, and ventricularpacing pulses are preferably supplied simultaneously to the twoventricular pace/sense electrodes if an R-wave is not sensed by eitherventricular sense amplifier before the AV delay times out.

A "double atrial, triple chamber" pacing system is described in the '161and '867 patents for treating dysfunctional atrial conduction using aprogrammable DDD pacemaker for pacing both atria simultaneously when anatrial sensed event is detected from either chamber or at the expirationof a V-A escape interval. The IPG includes atrial sense amplifierscoupled to atrial pace/sense electrodes positioned with respect toelectrode sites in or adjacent the right and left atria and aventricular sense amplifier coupled to ventricular pace/sense electrodeslocated in or on the right ventricle. In the '161 patent, ventricularpacing pulses are applied to the ventricular pace/sense electrodes atthe end of an AV delay timed from the atrial paced events unless thesensed atrial rate exceeds a rate limit. In the '867 patent, a fall backmode is commenced to limit the ventricular pacing rate if the sensedP-waves are deemed "premature". Clinical experience in use of doubleatrial, three chamber, pacing systems appears in abstracts by Daubert etal., including "Permanent Dual Atrium Pacing in Major IntratrialConduction Blocks: A Four Years Experience" appearing in PACE (Vol. 16,Part II, NASPE Abstract 141, p. 885, April 1993). In these systems,atrial pacing pulses are delivered simultaneously in a triggered mode toboth atria that is wasteful of electrical energy and fails to maintain aphysiologic delay between the evoked depolarizations of the atria.

Further clinical experience with two, three and four heart chamberpacing is also reported by Daubert et al. in "Permanent Left VentricularPacing With Transvenous Leads Inserted Into The Coronary Veins"appearing in PACE (Vol. 21, Part II, pp. 239-245, January 1998). In thetwo heart chamber context, Daubert et al. report implanting conventionalDDDR IPGs with the atrial pace/sense terminals coupled to a leftventricular lead having pace/sense electrodes located in relation to theleft ventricle. The ventricular pace/sense terminals were coupled toright ventricular leads having pace/sense electrodes located in relationto the right ventricle. The IPG was programmed to operate in the VVIRmode with short AV delays, e.g. 30 ms, for timing delivery of a pacingpulse to the right ventricle when an R-wave was first sensed in or apacing pulse was delivered to the left ventricle at the end of theprogrammed V-A escape interval. In this bi-ventricular pacing system,ventricular pacing pulses were not delivered in a triggered mode to bothventricles, but only the conduction delay from the left ventricle to theright ventricle could be programmed.

Daubert et al. also report use of a "double ventricular, triple chamber"pacing system in this article using DDDR IPGs having the atrialterminals coupled with the atrial pacing lead and the ventricularterminals coupled through an adaptor to two ventricular pacing leads.The pace/sense electrodes of the atrial pacing lead were implantedapparently in relation to the right atrium and the pace/sense electrodesof the ventricular pacing leads were implanted in relation to the rightand left ventricles. The DDDR IPG was programmed in the DDDR mode toprovide simultaneous pacing of the right and left ventricles at the endof an A-V delay timed from an atrial paced event at the expiration ofthe V-A pacing escape interval or an atrial sensed event occurringduring the V-A escape interval. In this system, the simultaneousdelivery of ventricular pacing pulses to both ventricles is wasteful ofelectrical energy and fails to maintain a physiologic delay between theevoked depolarizations of the ventricles.

A four chamber DDD pacing system providing right and left chamber pacingand sensing is described in this Daubert et al, article and in anarticle by Cazeau et al. entitled "Four Chamber Pacing in DilatedCardiomyopathy" appearing in PACE (Vol. 17, Part II, pp. 1974-1979,November 1994). In these four chamber systems, right and left atrialleads are coupled "in series" through a bifurcated bipolar adaptor withatrial pace/sense connector block terminals, and right and leftventricular leads are coupled "in series" through a bifurcated bipolaradaptor with ventricular pace/sense connector block terminals. Rightatrial and right ventricular leads are connected to the cathode ports,while left atrial and left ventricular leads are connected to the anodeports of each bipolar bifurcated adaptor. The IPG is programmed in theDDD mode and in a bipolar pacing mode with a common AV delay that iscommenced by the delivery of atrial pacing pulses. The earliest right orleft atrial sensed event (i.e., P-wave) within a V-A escape interval orthe expiration of the V-A escape interval triggers delivery of atrialpacing pulses to both of the pace/sense electrodes in both atrialchambers through the series connected, right and left atrial leads. Itappears that the sensing "in series" of either a right or leftventricular R-wave across the right and left pace/sense electrode pairduring the AV delay terminates the AV delay and triggers delivery ofventricular pace pulses across the right and left pace/sense electrodepair. In this pacing system, both atrial and ventricular pacing pulsesare delivered to both atria and both ventricles on sensing a P-wave andon sensing an R-wave, respectively, which is wasteful of electricalenergy. And, the resulting simultaneous depolarization of the right andleft atria or the right and left ventricles is not physiologicallybeneficial in many instances

In these approaches, the atrial and/or ventricular pace/sense electrodesare located in a variety of locations and manner with respect to theright and left atria and/or right and left ventricles. In the '688patent, one ventricular pace/sense electrode is located at the distalend of an endocardial lead introduced deeply into the great veinextending from the coronary sinus to place it adjacent to the leftventricle. It is also known that the pace/sense electrode of anendocardial lead can be placed closer to the entrance to the coronarysinus and adjacent the left atrium. Such an approach is shown in theabove-referenced Cazeau et al. article and in an abstract by Daubert etal., "Renewal of Permanent Left Atrial Pacing via the Coronary Sinus",appearing in PACE (Vol. 15, Part II, NASPE Abstract 255, p. 572, April1992), incorporated herein by reference. Epicardial screw-in, pace/senseelectrodes can also be placed epicardially on the right and leftventricles because the myocardial walls are thick enough to not beperforated in the process as also shown in the above-referenced Cazeauet al. article. In addition, a bi-ventricular pacemaker is proposed inthe above-incorporated '259 patent having an array of ventricularpace/sense electrodes fitting about the apex of the heart to provide aplurality of usable epicardial pacing and/or sensing electrode sitesabout the apical region of the heart.

These approaches show promise in restoring the synchronous contractionsof the right and left heart chambers in diseased hearts havingsignificant conduction disturbances of the right and left heartdepolarization waves but fail to preserve right and left heart synchronyin a physiologic manner. Significant conduction disturbances between theright and left atria can result in left atrial flutter or fibrillationthat can be suppressed by pacing the left atrium synchronously withright atrial pacing of sensing of P-waves. And, left atrial and leftventricular cardiac output can be significantly improved when left andright chamber synchrony is restored, particularly in patients sufferingfrom dilated cardiomyopathy.

SUMMARY OF THE INVENTION

The present invention is therefore directed to providing symmetricallyoperating right and left heart chamber pacing systems and methods ofoperation in two upper heart chambers or two lower heart chambers orthree or four heart chambers that provide synchronous pacing of rightand left heart chambers as needed. Such pacing systems of the presentinvention overcome the problems and limitations of the multiple chamberpacing systems described above and provide a great deal of flexibilityin tailoring the delivered pacing therapy to needs of the individualpatient's heart.

The present invention is also characterized herein as comprisingmulti-channel pacing systems having two, three or four pacing channels;each pacing channel includes a sense amplifier and pace output pulsegenerator coupled through a pacing lead with the pace/sense electrodesof each pacing channel located in relation to a heart chamber.

In accordance with the present invention, the synchronous pacing of oneof the right and left heart chambers is provided on demand followingexpiration of programmable conduction delay windows (CDWs) that arestarted by both a paced event and a sensed event first occurring in theother of the right and left heart chambers. The delivery of the pacingpulse is inhibited by a sensed event detected in the other of the rightand left heart chambers before the expiration of the CDW started by thepaced event or sensed event first sensed in the other heart chamber.Advantageously, battery energy is not depleted by triggered pacing inthe heart chamber where the spontaneous depolarization is first sensed.

The CDWs can be of the same length but preferably are programmable inlength to take into account the type of event (paced event or sensedevent) that commences them and the locations of the pace/senseelectrodes with relation to the right and left heart chambers and theirseparation from one another. The programmed CDWs advantageously providethe optimum physiologic timing to sense depolarizations that areconducted to the second heart chamber from the first heart chamber thatspontaneously depolarizes or is paced and to deliver a pacing pulse ifthe depolarization is not conducted within the CDW. The programmable CDWtimes can be selected to approximate normal, physiologic conductiondelays or to provide a sequence of evoked depolarizations through pacingof the right and left heart chambers that compensates for a defect ofthe heart, e.g., a defective cardiac valve function.

More particularly, preferably a spontaneous, non-refractory, sensedevent first sensed in one heart chamber before the expiration of anescape interval or an AV delay starts a sensed event CDW (CDW^(S)) forthe sensing of a conducted depolarization in the other heart chamber. Apacing pulse delivered to one heart chamber at the expiration of anescape interval or an AV delay evokes a paced event and starts a pacedevent CDW (CDW^(P)) for the sensing of a conducted depolarization in theother heart chamber. Pacing in the other heart chamber is inhibited if aconducted depolarization is sensed as a sensed event within the CDW^(S)or the CDW^(P). Similarly, a pacing pulse is delivered to that heartchamber at the end of the CDW^(S) or the CDW^(P) if the CDW^(S) or theCDW^(P) times out without sensing a sensed event in that heart chamber.Each CDW^(S) and CDW^(P) for timing conduction of spontaneous or evokeddepolarizations from the right and left heart chambers to the left andright heart chambers, respectively, is separately programmable inlength. The provision of the separate sense CDW^(S) and pace CDW^(P)allows compensation for conduction delay differences that may exist inconduction of a depolarization that spontaneously occurs or is evoked bydelivery of a pacing pulse. Such differences can arise due to physiologyand/or arise from differences in the start of the evoked depolarizationin response to the pace pulse applied to the first pair of pace/senseelectrodes.

In the context of a two channel, bi-atrial or bi-ventricular, pacingsystem employing the present invention, an escape interval for timingdelivery of pacing pulses in a bradycardia condition or the absence ofany spontaneous depolarizations is provided. The escape interval ispreferably timed from a previous paced event or sensed event in selectedone heart chamber or a sensed event first occurring in either heartchamber. Thus, an asymmetry is introduced by the selection of the heartchamber to be first paced at the expiration of the escape interval.Advantageously, the selection of the heart chamber to be first paced andto commence the CDW^(P) can be programmed to provide a pacing order thatcompensates for a cardiac defect. Or it can be programmed to provide themost physiologic pacing mimicking a normal electrical activationsequence between the pace/sense electrode location in relation to thatselected heart chamber and the pace/sense electrode location in relationto the other heart chamber. Typically, the patient's heart would beassessed to determine which of the right or left heart chambers exhibitsa normal electrical activation sequence, and that heart chamber would beselected to be first paced at the expiration of the pacing escapeinterval. For example, the heart chamber exhibiting a normal activationsequence would be selected to be first paced at the expiration of theescape interval in a heart that exhibits IACD, LBBB, or RBBB.

The present invention is also implemented in three or four channelpacing systems wherein AV synchrony is maintained between the upper andlower heart chambers and right and left heart chamber synchrony ismaintained between one or both sets of the right and left heartchambers. AV synchrony is maintained between the three or four atrialand ventricular heart chambers by one or more programmable AV delaytimed from an atrial paced or sensed event from the single or a selectedone of the atrial pacing channels. A V-A escape interval is timed from aventricular paced or sensed event from the single one or a selected oneof the ventricular pacing channels. In each case, where right and leftheart pacing channels are provided or programmed for use, a pacing pulseis delivered to one of the heart chambers at the expiration of the V-Aescape interval or the AV delay. An atrial or a ventricular paced eventCDW^(P) is started for the sensing of a conducted depolarization in theother heart chamber. An atrial or a ventricular sensed event CDW^(S) isstarted for the sensing of a conducted depolarization in the other heartchamber if a sensed event is detected within the V-A escape interval orthe AV delay. Pacing in the other heart chamber is inhibited if aconducted depolarization is sensed as a sensed event within the CDW^(S)or the CDW^(P). Similarly, a pacing pulse is delivered to that heartchamber at the end of the CDW^(S) or the CDW^(P) if the CDWs or theCDW^(P) times out without sensing a sensed event in that heart chamber.Each CDW^(S) and CDW^(P) for timing conduction of spontaneous or evokeddepolarizations from the right and left heart chambers to the left andright heart chambers, respectively, is separately programmable inlength.

In one three pacing channel embodiment, pace/sense electrodes arelocated in relation to either the right or left atrial heart chamber andboth ventricular heart chambers, and pacing and sensing is provided tothese heart chambers. In this embodiment, the AV delay is timed from anatrial paced event or sensed event, and the V-A escape interval can beprogrammed to be timed from either a right or left ventricular pacedevent or sensed event. In another three pacing channel embodiment,pace/sense electrodes are located in relation to both atrial heartchambers and to the right or left ventricular heart chambers, and pacingand sensing is provided to these heart chambers. In this embodiment, theAV delay is timed from a selected right or left atrial paced event orsensed event, and the V-A escape interval is timed from the ventricularpaced event or sensed event.

In a full four pacing channel embodiment, right and left, atrial andventricular sense amplifiers and pacing pulse output circuits areprovided for sensing and pacing in all four heart chambers. The right orthe left heart ventricular pacing channels are selected to controltiming of the V-A pacing escape interval, and the right or left atrialpacing channels are selected to time out the AV delay, therebyintroducing an asymmetry of operation. The full set of atrial andventricular CDW timers are not employed or are selectively programmed ONand OFF to take into account either the normal right heartchamber-to-left heart chamber or left heart chamber-to-right heartchamber conduction delays correlated to the controlling right or leftheart chamber.

The present invention also contemplates providing separatelyprogrammable AV delays which are started from both right and left atrialsensed and paced events, if both right and left atrial pacing channelsare provided in the multi-channel pacing system. Moreover, both sensedand paced AV (SAV and PAV) delays are separately programmable and arestarted by right and/or left atrial paced events and sensed events andare terminated by a selected right or left ventricular sensed event. Thecommencement of the V-A escape interval can also be selected to betriggered by a right or left ventricular paced event or sensed event.

For example, in a patient suffering from abnormal right atrial-to-leftatrial conduction delays, such as IACD or 2nd degree AV Block, the rightatrium is selected as controlling the AV delay, and the right ventricleis selected as controlling the V-A escape interval. A left atrialCDW^(S) that is programmed in length is started upon detection of aspontaneous intrinsic right atrial depolarization during the V-A escapeinterval, and a SAV delay is started. Similarly, a left atrial CDW^(P)that is programmed in length is started upon delivery of a right atrialpace pulse at the end of the V-A escape interval, and a PAV delay isstarted. The delivery of the left atrial pace pulse is inhibited if aleft atrial sensed event is detected during the time out of either theleft atrial CDW^(S) or the CDW^(P), and a left atrial pace pulse isdelivered if no atrial sensed event is detected before the left atrialCDW^(S) or the CDW^(P) times out. Subsequently, a ventricular pace pulseis delivered to the selected ventricular pace/sense electrodes if noventricular sensed event is detected before the SAV or the PAV delaytimes out.

Similarly, in a patient suffering from abnormal right ventricle to leftventricle conduction delays, such as IVCD or 2nd degree AV Block, theright atrium is again selected as controlling the AV delay, and theright ventricle is selected as controlling the V-A escape interval. Theappropriate SAV or PAV delay is started following either a right atrialsensed event occurring during the V-A escape interval or a right atrialpaced event at the end of the V-A escape interval. A left ventricularsensed CDW^(S) or paced CDW^(P) is started upon detection of aspontaneous intrinsic right ventricular sensed event during the SAV orPAV delay or upon time out of the SAV or PAV delay. The delivery of theleft ventricular pace pulse is inhibited if a left ventricular sensedevent is detected during the time out of either the CDW^(S) or theCDW^(P), and a left ventricular pace pulse is delivered if noventricular sensed event is detected before the CDW^(S) or the CDW^(P)times out.

These approaches advantageously avoid delivering pacing pulsessubstantially simultaneously to both the right and left heart chamberseither in a triggered mode or in a synchronized mode as set forth in theprior art. A pacing pulse is delivered synchronously following thepreceding sensed event or paced event at the termination of the CDW^(S)or CDW^(P) respectively. In certain patients suffering from congestiveheart failure, the synchronously paced heart tends to recover its normalelectrical activation sequence over time. Thus, this approach providesthat if the recovery does occur, then the sensing of the normallyconducted spontaneous or evoked depolarization inhibits the unnecessarydelivery of pacing pulses.

In the dual chamber approaches, comprehensive right and left, atrial andventricular synchronization is advantageously restored while thedelivery of pacing pulses is minimized. In effect, physiologicconduction patterns are realized, competitive stimuli are eliminated,and battery longevity is enhanced due to non-redundant delivery ofpacing pulses.

The present invention offers numerous advantages to patient's sufferingfrom advanced congestive heart failure and exhibiting IACD, LBBB, RBBB,and/or IVCD. The introduction of the endocardial and/or epicardial rightand left heart pacing leads and the implantation of the IPG areminimally invasive. Longevity is enhanced by the inhibition of thedelivery of pacing pulses by sensed events detected within therespective controlling CDWs. The various operating modes of the IPG andthe CDWs can be programmed during chronic implantation to adjust toobserved changes in the underlying electrical activation sequence as thepatient's condition improves or deteriorates.

The various embodiments of the present invention are preferablyimplemented into an implantable pulse generator and lead systemselectively employing right and left heart, atrial and/or ventricularleads. However, they may also be implemented into an external pulsegenerator coupled with right and left heart, atrial and/or ventricularleads traversing the patient's skin. The various embodiments areimplemented into an architecture that allows wide programmingflexibility for operating in the above-described symmetric, right andleft pacing channel configurations. Or asymmetric configurations can beconfigured in hard wired two, three and four channel circuitry or byselective programming of the active right and left pacing channels. Theatrial channel that commences the SAV and PAV delays and the ventricularchannel that terminates the SAV and PAV delays and controls the timingof the V-A escape interval can also be hard wired or programmed.

In order to realize the above configurations and the advantages flowingtherefrom, the present invention preferably (but not necessarily)utilizes a low impedance field density clamp (FDC) sense amplifier whichuses active detection circuitry to monitor the amount of currentsupplied to a selected pace/sense electrode. The supplied currentchanges the surface charge density to compensate for theelectrode-electrolyte disturbance caused by the passage of a cardiacdepolarization wavefront. This form of sensing is most sensitive tochanges in charge distribution in a small volume of tissue locatedadjacent to the pace/sense electrode. This form of FDC sensing thereforeis not strongly affected by far-field pace events, in contrast to highinput impedance sense amplifiers. Thus, the delivery of a pace pulse tothe pace/sense electrodes located in the left or right heart chamberwill not mask a naturally conducted depolarization wave passing thepace/sense electrodes in the other heart chamber when it is sensed bythe FDC sense amplifier coupled with those pace/sense electrodes.

In the context of a bi-atrial or bi-ventricular pacemaker, or both, theFDC sense amplifier is capable of detecting a naturally conducteddepolarization wave within a wide range of programmed CDW times.Moreover, preferably (but not necessarily) the pacing output circuitsare also configured as FDC circuits to generate the pacing pulses.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, advantages and features of the presentinvention will be more readily understood from the following detaileddescription of the preferred embodiments thereof, when considered inconjunction with the drawings, in which like reference numerals indicateidentical structures throughout the several views, and wherein:

FIG. 1 is an illustration of transmission of the cardiac depolarizationwaves through the heart in a normal electrical activation sequence;

FIG. 2 is a schematic diagram depicting a two channel, bi-atrial pacingsystem in which the present invention is implemented;

FIG. 3 is a schematic diagram depicting a two channel, bi-ventricularpacing system in which the present invention is implemented;

FIG. 4 is a simplified block diagram of the circuitry of the presentinvention for the two channel, right and left heart chamber, IPGemployed in the systems of FIGS. 2 and 3;

FIG. 5 is a schematic diagram depicting a three or four channel,bi-atrial and/or bi-ventricular, pacing system in which the presentinvention is implemented;

FIGS. 6 and 7 collectively are a simplified block diagrams of oneembodiment of IPG circuitry of the present invention employed in thesystem of FIG. 5 for providing four pacing channels or selectivelyprogramming three pacing channels for selectively pacing right and left,upper and lower, heart chambers; and

FIG. 8 is a simplified block diagram of a further embodiment of amulti-channel pacing system that can be configured to function as a twochannel, three channel or four pacing channel pacing system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, references are made toillustrative embodiments for carrying out the invention. It isunderstood that other embodiments may be utilized without departing fromthe scope of the invention. For example, the invention is disclosed inthe context of two channel pacing system operating in demand andtriggered pacing modes for restoring synchrony in depolarizations andcontraction of left and right heart chambers for treating bradycardia inthose chambers. The invention is also disclosed in the context of a fourchannel pacing system having an AV synchronous operating mode forrestoring right and left heart chamber depolarization synchrony of theupper and lower heart chambers. The four channel pacing system isconfigurable to function as a three channel pacing system by selectivelydisabling one of the upper or lower pacing channels and associated logiccircuitry for timing the CDW^(S) and CDW^(P). It should be appreciatedthat the present invention may be utilized to suppress atrialtachyarrhythmias noted in the above-incorporated Daubert articles andmay in general be incorporated into an anti-tachyarrhythmia systemincluding specific high rate pacing and cardioversion shock therapiesfor providing staged therapies to treat a diagnosed arrhythmia. It willalso be appreciated that the two channel, three channel or four channelpacing systems and methods described herein in detail can be implantedand employed in treatment of an electrical conduction disturbance in asingle heart chamber or between two heart chambers.

FIG. 1 is an illustration of transmission of the cardiac depolarizationwaves through the right atrium (RA), left atrium (LA), right ventricle(RV) and left ventricle (LV) of heart 10 in a normal electricalactivation sequence at a normal heart rate with the conduction timesexhibited thereon in seconds. The cardiac cycle commences normally withthe generation of the depolarization impulse at the Sino-Atrial (SA)Node in the right atrial wall and its transmission through the atrialconduction pathways of Bachmann's Bundle and the Internodal Tracts atthe atrial level into the left atrial septum. The RA depolarization wavereaches the Atrio-ventricular (AV) node and the atrial septum withinabout 40 msec and reaches the furthest walls of the RA and LA withinabout 70 msec, and the atria complete their contraction as a result. Theaggregate RA and LA depolarization wave appears as the P-wave of thePQRST complex when sensed across external ECG electrodes and displayed.The component of the atrial depolarization wave passing between a pairof unipolar or bipolar pace/sense electrodes, respectively, located onor adjacent the RA or LA is also referred to as a sensed P-wave.Although the location and spacing of the external ECG electrodes orimplanted unipolar atrial pace/sense electrodes has some influence, thenormal P-wave width does not exceed 80 msec in width as measured by ahigh impedance sense amplifier coupled with such electrodes. A normalnear field P-wave sensed between closely spaced bipolar pace/senseelectrodes and located in or adjacent the RA or the LA has a width of nomore than 60 msec as measured by a high impedance sense amplifier.

The depolarization impulse that reaches the AV Node is distributedinferiorly down the bundle of His in the intraventricular septum after adelay of about 120 msec. The depolarization wave reaches the apicalregion of the heart about 20 msec later and is then travels superiorlythough the Purkinje Fiber network over the remaining 40 msec. Theaggregate RV and LV depolarization wave and the subsequent T-waveaccompanying re-polarization of the depolarized myocardium are referredto as the QRST portion of the PQRST cardiac cycle complex when sensedacross external ECG electrodes and displayed. The highest amplitudecomponent of the QRS ventricular depolarization wave passing between apair of unipolar or bipolar pace/sense electrodes, respectively, locatedon or adjacent the RV or LV is referred to as the sensed R-wave.Although the location and spacing of the external ECG electrodes orimplanted unipolar ventricular pace/sense electrodes has some influence,the normal R-wave width does not exceed 80 msec in width as measured bya high impedance sense amplifier. A normal near field R-wave sensedbetween closely spaced bipolar pace/sense electrodes and located in oradjacent the RV or the LV has a width of no more than 60 msec asmeasured by a high impedance sense amplifier.

The typical normal conduction ranges of sequential activation are alsodescribed in the article by Durrer et al., entitled "Total Excitation ofthe Isolated Human Heart", in CIRCULATION (Vol. XLI, pp. 899-912, June1970). This normal electrical activation sequence becomes highlydisrupted in patients suffering from advanced congestive heart failureand exhibiting IACD, LBBB, RBBB, and/or IVCD. These conduction defectsexhibit great asynchrony between the RV and the LV due to conductiondisorders along the Bundle of His, the Right and Left Bundle Branches orat the more distal Purkinje Terminals. Typical intra-ventricularpeak--peak asynchrony can range from 80 to 160 msec or longer. In RBBBand LBBB patients, the QRS complex is widened far beyond the normalrange to from >120 msec to 250 msec as measured on surface ECG. Thisincreased width demonstrates the lack of synchrony of the right and leftventricular depolarizations and contractions.

In accordance with the present invention, a method and apparatus isprovided to restore the depolarization sequence of FIG. 1 and thesynchrony between the right and left, atrial and ventricular heartchambers that contributes to adequate cardiac output. This restorationis effected through providing optimally timed cardiac pacing pulses toeach heart chamber as necessary and to account for the particularimplantation sites of the pace/sense electrodes in relation to eachheart chamber.

As noted in the above-referenced, commonly assigned, U.S. Pat. No.5,902,324, it has been common in the prior art to use very highimpedance P-wave and R-wave sense amplifiers to amplify the voltagedifference signal which is generated across the pace/sense electrodes bythe passage of a cardiac depolarization. The high impedance senseamplifiers use high gain to amplify the low amplitude signals and relyon pass band filters, time domain filtering and amplitude thresholdcomparison to discriminate a P-wave or R-wave from background electricalnoise. Moreover, the sense amplifiers are uncoupled from the pace/senseelectrodes during blanking periods of up to 100 msec after delivery of apacing pulse to any of the pace/sense electrodes of the pacing system toavoid saturation of the sense amplifiers.

The present invention as described hereafter preferably uses lowimpedance FDC sense amplifiers, as described in the above-referenced,commonly assigned, U.S. Pat. No. 5,902,324, to be able to time outrelatively short pace and sense CDWs. The FDC sense amplifier outputpulses developed in response to a P-wave or R-wave passing by bipolarpace/sense electrodes are less than 10 msec in width, rather than therelatively long, 60-80 msec, P-waves and R-wave pulses sensed using thehigh impedance sense amplifiers. The FDC sense amplifiers provide verynarrow output pulses as the P-wave or R-wave passes by the pace/senseelectrodes coupled thereto and stabilize rapidly so that closely spaced,successive depolarization wavefronts passing by the pace/senseelectrodes can be detected and distinguished from one another. Moreover,right and left heart chamber sense amplifier blanking intervals can beshortened to about the width of the pacing pulses which is typically0.5-1.0 msec and up to about 10 msec. The blanking intervals can beminimized because of the ability of the right and left heart FDC senseamplifiers to discriminate between a pacing pulse artifact reflectedacross the pace/sense electrode pair and any closely following cardiacdepolarization wavefront. Preferably, the blanking intervals areprogrammable so that they can be tailored after implantation andminimized to reflect the cardiac conduction conditions of the patient'sheart.

FIG. 2 is a schematic representation of an implanted, two channelcardiac pacemaker of the above noted types for restoring synchronouscontractions of the right and left atria. In FIG. 2, heart 10 includesthe upper heart chambers, the right atrium (RA) and left atrium (LA),and the lower heart chambers, the right ventricle (RV) and leftventricle (LV) and the coronary sinus (CS) extending from the opening inthe right atrium laterally around the atria to form the great vein thatextends further inferiorly into branches of the great vein. Thepacemaker IPG 14 is implanted subcutaneously, between the skin and theribs. Bipolar, endocardial RA lead 16 and bipolar endocardial LA CS lead22 are passed through a vein into the RA chamber of the heart 10 andinto the CS to extend alongside the LA chamber. The RA lead 16 is formedwith an in-line connector 13 fitting into a bipolar bore of IPGconnector block 12 that is coupled to a pair of electrically insulatedconductors within lead body 15 and connected with distal tip RApace/sense electrode 19 and proximal ring RA pace/sense electrode 21.The distal end of the RA lead 16 is attached to the RA wall by anattachment mechanism 17. The LA CS lead 22 is formed with an in-lineconnector 24 fitting into a bipolar bore of IPG connector block 12 thatis coupled to a pair of electrically insulated conductors within leadbody 26 and connected with distal ring LA CS pace/sense electrode 30 andproximal ring LA CS pace/sense electrode 28. The distal end of the LA CSlead 26 is extended into the CS to position the LA CS pace/senseelectrodes optimally with respect to the adjacent LA wall.

In operation, a P-wave sensed across either pair or one selected pair ofthe atrial pace/sense electrodes 17, 19 or 28, 30, is employed to resetthe current A--A atrial escape interval and to start an atrial senseCDW^(S) time. The A--A escape interval is typically timed from the rightatrial paced and sensed events, but it can the left atrial paced andsensed events in appropriate circumstances. The right and left atrialsense CDW^(S) lengths in msec are programmed to reflect the normalconduction delays of spontaneous atrial depolarizations between theatrial pace/sense electrodes 17, 19 and 28, 30 in a normal electricalactivation sequence or to respond to a reverse activation sequence. Anatrial pace pulse is delivered to the other pair of atrial pace/senseelectrodes 17, 19 or 28, 30 to synchronize the right and left atrialdepolarizations if the appropriate atrial CDW^(S) time times out withoutthe sensing of the P-wave at that other pair of the pace/senseelectrodes. If the A--A atrial escape interval times out, then theatrial pace pulse is typically first delivered across the RA pace/senseelectrodes 17, 19, and the paced atrial CDW^(P) time is commenced. Anatrial pace pulse is delivered to the LA CS pace/sense electrodes 28, 30if the paced atrial CDW^(P) times out without the sensing of the P-waveat the LA CS pace/sense electrodes 28 and 30.

FIG. 3 is a schematic representation of an implanted, two channelcardiac pacemaker of the above noted types for restoring synchronouscontractions of the right and left ventricles. Bipolar, endocardial LVCS lead 42 is passed through a vein into the RA chamber of the heart 10,into the CS and then inferiorly in the great vein and cardiac veinsextending therefrom to extend the distal ring pace/sense electrodes 48and 50 alongside the LV chamber. Bipolar, endocardial RV lead 32 ispassed through the vein into the RA chamber of the heart 10 and into theRV where its distal ring and tip pace/sense electrodes 38 and 40 arefixed in place in the apex or in the interventricular septum by a distalattachment mechanism 52. The RV lead 32 is formed with an in-lineconnector 34 fitting into a bipolar bore of IPG connector block 12 thatis coupled to a pair of electrically insulated conductors within leadbody 36 and connected with distal tip pace/sense electrode 40 andproximal pace/sense ring electrode 38. The LV CS lead 42 is formed withan in-line connector 44 fitting into a bipolar bore of IPG connectorblock 12 that is coupled to a pair of electrically insulated conductorswithin lead body 46 and connected with distal ring pace/sense electrode50 and proximal pace/sense ring electrode 48. The distal end of the LVCS lead 42 is extended into the CS to position the ring electrodesoptimally with respect to the adjacent LV wall.

In operation, the R-wave sensed across one selected pair of theventricular chamber pace/sense electrodes 38, 40 or 48, 50 is employedto reset the current V--V ventricular escape interval and to start aventricular CDW^(S). The V--V escape interval is typically timed fromthe right ventricular paced and sensed events, but it can be timed fromthe left ventricular paced and sensed events in appropriatecircumstances. The right and left ventricular CDW^(S) lengths in msecare programmed to reflect the normal conduction delays between theventricular pace/sense electrodes 38, 40 and 48, 50 in a normalelectrical activation sequence and in a reverse activation sequence. Aventricular pace pulse is delivered to the other pair of ventricularpace/sense electrodes to synchronize the right and left ventriculardepolarizations if the right or left ventricular CDW^(S) times outwithout the sensing of the R-wave at the other pair of the pace/senseelectrodes 38, 40 or 48, 50. If the V--V ventricular escape intervaldoes time out, then the ventricular pace pulse is typically firstdelivered across the RV pace/sense electrodes 38 and 40, and theventricular pace CDW^(P) is commenced. A ventricular pace pulse isdelivered to the LV CS pace/sense electrodes 48 and 50 if theventricular CDW^(P) times out without the sensing of the R-wave at theLV CS pace/sense electrodes 48 and 50. As described further below, thisorder can be reversed in appropriate instances.

These illustrated RA and LA and RV and LV pace/sense leads and electrodelocations are merely exemplary of possible leads and electrode locationsthat can be employed in the practice of these embodiments of the presentinvention. It will be understood that one or more of the other types ofendocardial and epicardial leads and pace/sense electrodes located in orabout the right and left chambers of the heart can be substituted forthose illustrated in FIGS. 2 and 3 and described above.

In FIG. 4, the right heart chamber (RHC) and left heart chamber (LHC)designations are employed to embrace both bi-atrial and bi-ventricularcontexts of use of a two channel pacing system of the present invention.Thus, FIG. 4 is a simplified block diagram of a two channel pacingsystem circuit comprising RHC circuitry 100 and LHC circuitry 200 andcommon components that can be employed to provide the pacing and sensingfunctions in a two channel, bi-atrial, pacemaker of FIG. 2 orbi-ventricular pacemaker of FIG. 3. Timing and control of the RHC andLHC circuitry 100 and 200 is realized through the software routinesmaintained in a microcomputer comprising the microprocessor 108, RAM/ROMchip 110, and DMA circuit 112 and in a pacer timing/logic circuit 120coupled therewith. Operating modes and parameter values are programmedinto RAM in RAM/ROM chip 110 through use of the external programmer 90that transmits RF telemetry transmissions through the patient's skin toan antenna 106 and the RF telemetry transmitter/receiver 102 coupledwith pacer timing/logic circuit 120. Such transcutaneous RF telemetry iswell known in the art and allows programming of the operating modes, theA--A and V--V escape intervals and other timing and control intervalsincluding the left and right channel CDW^(S) and CDW^(P) time lengths inaccordance with the present invention.

Interconnections are provided between the RHC and LHC pacing and sensingcircuitry 100 and 200 to perform the timing out of each CDW^(S) andpacing if necessary to assure that the right and left heart chambers aredepolarized and contract in the desired time relation to one another.The two channel IPG circuit of FIG. 4 is intended to comprehensivelyillustrate particular bi-atrial and bi-ventricular IPG circuits that maybe employed to practice the various embodiments of the invention. Thedepicted RHC and LHC pacing and sensing circuitry 100 and 200 is fullysymmetric. It will be understood that asymmetric two channel IPGcircuits can be derived from the comprehensive two channel IPG circuitillustrated in FIG. 4 that function to treat unduly prolonged RHC-to-LHCconduction delays or LHC-to-RHC conduction delays. Such asymmetric twochannel IPG circuits can be effected either by selectively disabling(through programming commands) or by simply physically eliminatingunused components of the RHC or LHC circuitry 100 or 200. The componentsand logical interconnections illustrated in FIG. 4 are first described,and then the possible modifications are described.

With respect to the RHC circuitry 100, the RHC pace/sense terminals inthe connector block 12 are coupled to the input terminals of RHC FDCamplifier 126 and to the output terminals of the RHC pacing pulse outputcircuit 134. Operating parameters of the RHC FDC amplifier 126 and theRHC pacing pulse output circuit 134 are set by programmed parametervalues and operating modes provided on data/control bus 122. The RHCpacing pulse output circuit 134 delivers an RHC pacing pulse to the RHCterminals at a programmed pulse width and amplitude in response to anRHC PACE signal that is passed through OR gate 116. The RHC PACE signalis either the RHC pace trigger (RHC PT) signal generated by the RHC CDWtimer 230 or the RHC escape interval pace trigger (RHC EI PT) signalgenerated by the escape interval timer in pacer timing/logic circuit120.

An RHC BLANK signal is applied on line 118 to the RHC FDC amplifier 126during and for a short period of less than 10 msec following delivery ofan RHC or an LHC pacing pulse. The RHC BLANK signal is provided by RHCblanking circuit 136 in response to an RHC blanking trigger signalpassed through OR gate 114 to the RB input. The OR gate 114 provides theRHC BLANK AND LHC BLANK trigger signals when a pacing pulse is triggeredand delivered by either of the RHC and LHC pace output circuits 134 and234. The OR gate 114 passes the RHC PACE and LHC PACE output signals ofOR gate 116 and OR gate 216 which in turn pass the RHC pace trigger (RHCPT) and LHC pace trigger (LHC PT) signals that are generated by the timeout of the escape interval or the programmable CDW^(S) and CDW^(P)times. The duration of the RHC BLANK signal is programmed into RAM/ROMchip 110 and retrieved and applied on data/control bus 122 to the RBPinput of the programmable RHC blanking circuit 136. The RHC FDCamplifier 126 is thereby rendered incapable of responding to an RHCdepolarization signal during the short time that an RHC BLANK signal isapplied to it on line 118.

When the RHC BLANK signal is not present, the RHC FDC amplifier 126responds to an RHC cardiac depolarization by providing a high amplitude,short duration sensed event RHC (SERHC) signal on line 132. The RHC FDCamplifier 126 responds to an RHC cardiac depolarization sensed acrossthe RHC pace/sense electrodes. The RHC cardiac depolarization canoriginate spontaneously in the RHC or can originate spontaneously in theLHC or be evoked by an LHC pace pulse delivered to the LHC pace/senseelectrodes and, in either case, be conducted to the RHC pace/senseelectrodes in the RHC. The SERHC signal is provided to the programmableLHC CDW timer 130 to start timing out the programmed LHC CDW^(S) time ifthe LHC CDW timer 130 is not inhibited at the time. The SERHC signal isalso applied to the RHC inhibit input of the RHC pacing output circuit134 to prevent it from operating and to the reset logic within pacertiming/logic circuit 120 to reset the escape interval timer. The escapeinterval timer is restarted by either the SERHC signal or the SELHCsignal to generate either the RHC EI PT signal or the LHC escapeinterval pace trigger (LHC EI PT) signal on its expiration. The SERHCsignal is also passed through the NOR gate 135 as the RHC CDW INHIBITsignal to reset and inhibit the RHC CDW timer as described below.

The LHC CDW^(S) and CDW^(P) time lengths are programmed into RAM/ROMchip 110 and retrieved and applied on data/control bus 122 to the TDinput to the programmable LHC CDW timer 130. The programmable LHC CDWtimer 130 starts timing out the programmed LHC CDW^(S) time on receiptof the SERHC signal at start input S1. In addition, the programmable LHCCDW timer 130 starts timing out the programmed LHC CDW^(S) time at thetime that the RHC PACE signal is applied to the RHC pacing outputcircuit 134. This is effected by applying the RHC EI PT signal to aseparate start input S2. It will be understood that the LHC CDW timer130 may include redundant timers and selection logic to provide that afirst LHC CDWs time may be started upon application of the SERHC signalat start input S1 and a second LHC CDW^(P) time may be started uponapplication of the RHC EI PT signal to the start input S2. It will alsobe understood that the LHC CDW timer 130 may include programmable logicthat responds to a programmed in selection command to disable responseof the LHC CDW timer 130 to one or both of the SERHC and the RHC EI PTsignals.

The programmable LHC CDW timer 130 generates an LHC PT signal if the LHCFDC amplifier 226 does not detect an LHC depolarization wave andgenerate the left heart chamber sensed event signal (SELHC) and LHCRESET command on line 232 before the programmed RHC CDW^(S) or CDW^(P)is timed out. The LHC PT signal is applied through OR gate 216 to theLHC PACE input of the LHC pacing pulse output circuit 234 which providesan LHC pacing pulse to the LHC terminals of the connector assembly 12.In this manner, the LHC pacing pulse is applied to the LHC terminals ofthe connector assembly 12 following the lapse of the LHC CDW^(P) orCDW^(S) following an RHC pacing pulse or a SERHC signal, respectively,to restore RHC-to-LHC synchrony.

The timing out of the programmable LHC CDW^(S) or CDW^(P) time by theLHC CDW timer 130 is halted and further triggering of the LHC timer 130is inhibited by an LHC CDW INHIBIT signal applied to the inhibit (INH)input of LHC CDW timer 130. The LHC CDW INHIBIT signal is of a durationthat is longer than any programmed CDW time but shorter than the pacingescape interval. The LHC CDW INHIBIT signal prevents the LHC CDW timer130 from being restarted in response to a SERHC signal generated onsensing a depolarization that is conducted from the LHC pace/senseelectrodes to the RHC pace/sense electrodes that is itself evoked by theLHC PT signal that it delivered to NOR gate 216. Consequently, the LHCPT signal is passed through the NOR gates 216 and 235 and applied to theINH input of LHC CDW timer 130. Similarly, the LHC CDW INHIBIT signal isgenerated by passage of the LHC EI PT signal or the SELHC signal throughNOR gate 235 and applied to the INH input of the LHC CDW timer. Only theRHC CDW timer 230 should be started when these RHC paced and sensedevents occur.

The LHC signal sensing and pacing output circuitry 200, in conjunctionwith NOR gates 114, 116 and 135, is configured and functions in a mirrorimage fashion to the RHC signal sensing and pacing output circuitry 100described above. The LHC pace/sense terminals in the connector block 12are coupled to the input terminals of LHC FDC amplifier 226 and to theoutput terminals of the LHC pacing pulse output circuit 234. A LHC BLANKsignal is applied on line 218 to the LHC FDC amplifier 226 during theRHC PACE or LHC PACE signal as reflected through OR gate 114 and for ablanking time period thereafter. The LHC BLANK signal is provided by LHCblanking circuit 236 in response to an RHC blanking trigger signalgenerated by OR gate 114 and applied to the RB input. The duration ofthe LHC BLANK signal is programmed into RAM/ROM chip 110 and retrievedand applied on data/control bus 122 to the LBP input of the programmableLHC blanking circuit 236.

As in the case of the LHC CDW timer 130, it will be understood that theRHC CDW timer 230 includes redundant timers and selection logic to timethe sense RHC CDW^(S) started upon application of the SELHC signal atstart input S1 and a pace RHC CDW^(P) started upon application of theLHC EI PT signal to the start input S2. The programmable RHC CDW timer230 starts timing out the programmed RHC CDW^(P) time at the time thatthe LHC PACE signal is applied to the LHC pacing output circuit 234 ifit is not inhibited. It will also be understood that the RHC CDW timer230 may include programmable logic that responds to a programmed inselection command to disable response of the RHC CDW timer 230 to one orboth of the SELHC and the LHC EI PT signals.

The LHC FDC amplifier 226 responds to an LHC cardiac depolarizationsensed across the LHC pace/sense electrodes when it is not blanked by anLHC BLANK signal by providing a high amplitude, short duration sensedevent signal SELHC on line 232. The LHC cardiac depolarization canoriginate spontaneously in the LHC or can originate spontaneously in theRHC or be evoked by an RHC pace pulse delivered to the RHC pace/senseelectrodes and, in either case, be conducted to the LHC pace/senseelectrodes in the LHC. The SELHC signal is provided to the S1 input ofprogrammable RHC CDW^(S) timer 230 to start timing out the programmedRHC CDW^(S) time if it is not inhibited at the time. The SELHC signal isalso applied to the LHC INH input of the LHC pacing output circuit 234to prevent it from operating and to the reset logic within pacertiming/logic circuit 120 to reset the escape interval timer if theescape interval timer is programmed to respond to it. The SELHC signalis also applied as the INH input of the LHC CDW timer 130 through NORgate 235, although it is not actually timing out an LHC CDW time in thisscenario.

The programmable RHC CDW timer 230 generates an RHC PT signal at thetime out of the RHC CDW^(S) time if the RHC FDC amplifier 126 does notearlier detect an RHC depolarization wave and generate the SERHC signal.The RHC PT signal is applied through OR gate 116 to the RHC PACE inputof the RHC pacing pulse output circuit 134 which provides a pacing pulseto the RHC pace/sense terminals of the connector assembly 12. However,if the SERHC signal is generated during the RHC CDW^(S) time, it resetsthe RHC CDW timer 230 to terminate the RHC CDW time and inhibits theoperation of the RHC CDW timer 230 from being restarted for a presetinhibition period in the manner described above.

The sensing characteristics of the RHC and LHC FDC amplifiers 126 and226, the CDW^(S) and CDW^(P) times of the LHC and RHC CDW timers 130 and230 and the RHC and LHC pacing pulse output circuits 134 and 234 can beseparately programmed. The external programmer 90 is employed to providethe programmed modes and values via downlink telemetry with antenna 106and RF transmitter/receiver 102 that are decoded and stored in RAM/ROMchip 110 in a manner well known in the art. Thus, while there issymmetry in the right and left heart chamber pacing and sensingcircuitry, the operation can be made symmetric or asymmetric to optimizefunction in a given patient.

In the illustrated comprehensive two channel IPG circuit of FIG. 4, asingle escape interval timer can be programmed with an escape intervalvalue and programmed to generate the RHC EI PT signal or the LHC EI PTat the time out of the escape interval unless the escape interval isearlier restarted by a sensed RHC or LHC depolarization.

The normally functioning heart involves the depolarization andcontraction of the right atrium first, the left atrium second and theright and left ventricles after the AV delay time as shown above withrespect to FIG. 1. The interatrial conduction disturbances involveeither a prolonged delay that may approach or exceed the AV delay or acomplete dissociation of the right and left atrial contractions at allor certain heart rates. The interventricular conduction disturbancestypically involve a retardation of the depolarization wave through theleft ventricle outer wall which may be caused by damage to theconduction system and/or an enlarged heart muscle found in congestiveheart chamber. Whatever the cause, in the typical case to be treated,the right heart chamber(s) contracts first, followed by the contractionof the left heart chamber(s) after the prolonged conduction delay. Theconverse situation does not arise typically but can occur as a result ofpremature atrial contractions arising in the left atrium. Thus, in thiscase, the IPG circuit of FIG. 4 can be programmed to operate in anasymmetric manner wherein the use of the LHC CDW timer 230 and isprogrammed OFF by a programmed in command or is eliminated entirely.

For example, the two channel IPG circuit components are capable of beingprogrammed to respond to and treat unduly prolonged RHC-to-LHCconduction delays in the normal electrical activation sequence of FIG. 1that occur due to IACD, LBBB, IVCD, RV Ectopic foci conduction patterns,RV pacing conduction patterns. In these cases, programmed in modecommands disable the RHC CDW timer 230, and the reset logic isprogrammed to only employ the SERHC signal to reset the escape intervaltimer. In addition, the escape interval timer only generates the RHC EIPT signal.

However, it will be realized that the two channel IPG circuit componentsare capable of being programmed to respond to and treat unduly prolongedLHC-to-RHC conduction delays in a reverse electrical activation sequencethan the normal electrical activation sequence of FIG. 1 that occur dueto RBBB, IVCD, LV Ectopic foci conduction patterns, and LV pacingconduction patterns. In these cases, programmed in mode commands disablethe LHC CDW timer 130, and the reset logic is programmed to only employthe SELHC signal to reset the escape interval timer. In addition, theescape interval timer only generates the LHC EI PT signal. Of course,these configurations can be realized through a physical reduction of thecomponents and interconnections of the comprehensive two channel circuitof FIG. 4.

FIG. 5 is a schematic representation of an implanted, four channelcardiac pacemaker of the above noted types for restoring synchronouscontractions of the right and left atria and the right and leftventricles. The in-line connector 13 of RA lead 16 is fitted into abipolar bore of IPG connector block 12 and is coupled to a pair ofelectrically insulated conductors within lead body 15 that are connectedwith distal tip RA pace/sense electrode 19 and proximal ring RApace/sense electrode 21. The distal end of the RA lead 16 is attached tothe RA wall by a conventional attachment mechanism 17. Bipolar,endocardial RV lead 32 is passed through the vein into the RA chamber ofthe heart 10 and into the RV where its distal ring and tip RV pace/senseelectrodes 38 and 40 are fixed in place in the apex by a conventionaldistal attachment mechanism 41. The RV lead 32 is formed with an in-lineconnector 34 fitting into a bipolar bore of IPG connector block 12 thatis coupled to a pair of electrically insulated conductors within leadbody 36 and connected with distal tip RV pace/sense electrode 40 andproximal ring RV pace/sense electrode 38.

In this case, a quadripolar, endocardial LV CS lead 52 is passed througha vein into the RA chamber of the heart 10, into the CS and theninferiorly in the great vein to extend the distal pair of LV CSpace/sense electrodes 48 and 50 alongside the LV chamber and leave theproximal pair of LA CS pace/sense electrodes 28 and 30 adjacent the LA.The LV CS lead 52 is formed with a four conductor lead body 56 coupledat the proximal end to a bifurcated in-line connector 54 fitting into apair of bipolar bores of IPG connector block 12. The four electricallyinsulated lead conductors in LV CS lead body 56 are separately connectedwith one of the distal pair of LV CS pace/sense electrodes 48 and 50 andthe proximal pair of LA CS pace/sense electrodes 28 and 30.

In operation, a P-wave sensed across the RA pace/sense electrodes 17 and19 or the LA pace/sense electrodes 28 and 30 during the V-A escapeinterval timed from a preceding ventricular pacing pulse or R-wavesensed event is employed to start an AV delay and to start an LA CDW^(S)or an RA CDW^(S), respectively. An atrial pace pulse is delivered to theother pair of atrial pace/sense electrodes 17 and 19 or 28 and 30 if therespective LA or RA CDW^(S) times out without the sensing of the sameconducted P-wave at that other pair of the atrial pace/sense electrodes.

If the V-A atrial escape interval does time out without sensing a P-waveat either pair of atrial pace/sense electrodes 17 and 19 or 28 and 30,then the atrial pace pulse is typically first delivered across the RApace/sense electrodes 17 and 19, and the respective LA CDW^(P) time iscommenced. Then, an atrial pace pulse is delivered to the LA CSpace/sense electrodes 28 and 30 only if the LA CDW^(P) times out withoutthe sensing of the P-wave at those pace/sense electrodes. However, it isalso possible to program the reverse order of delivery so that the firstatrial pace pulse is delivered to the LA CS pace/sense electrodes 28 and30 at the expiration of the V-A atrial escape interval. Then, an atrialpace pulse is delivered to the RA pace/sense electrodes 17 and 19 onlyif the RA CDW^(P) time times out without the sensing of the P-wave atthe RA pace/sense electrodes.

It is proposed herein to employ separate programmable sense AV (SAV)delays that are employed depending on whether the first atrial sensedevent is sensed across the RA pace/sense electrodes 17 and 19 or the LACS pace/sense electrodes 28 and 30. Moreover, it is proposed to employseparate programmable paced AV (PAV) delays that are employed dependingon whether the first atrial pacing pulsed is delivered across the RApace/sense electrodes 17 and 19 or the LA CS pace/sense electrodes 28and 30. These separately programmable RSAV and LSAV delays and RPAV andLPAV delays are provided to take into account the particular locationsof the RA and LA pace/sense electrodes and the measured conduction timedelays between those locations and the locations of the RV and LVpace/sense electrodes. This approach employing separate programmableRSAV and LSAV delays and separate programmable RPAV and LPAV delays isdisclosed herein in reference to FIGS. 6 and 7 as one approach in whichthe present invention can be practiced. However, it will be understoodthat the present invention can be practiced employing a less complexapproach using only a single, programmable AV delay or just one SAVdelay and PAV delay.

Thus, in the preferred more complex case, an LSAV or RSAV or an LPAV orRPAV time is started on either sensing the first P-wave or on deliveryof the first atrial pacing pulse to either the left or right atrialheart chamber. An R wave sensed across either of the RV or LV CSpace/sense electrodes 38 and 40 or 48 and 50 during the AV time delay isemployed to reset the AV timer, to start a V-A escape interval, and tostart a respective LV CDW^(S) or RV CDW^(S). A ventricular pace pulse isdelivered to the other pair of RV or LV CS pace/sense electrodes 38 and40 or 48 and 50 if the LV CDW^(S) or RV CDW^(S) times out without thesensing of the R-wave at the other pair of the RV or LV CS pace/senseelectrodes.

Assuming that the normal activation sequence is sought to be restored, asingle AV delay corresponding to a normal AV conduction time from the AVnode to the bundle of His is programmed for use. If the AV delay timeout, then the ventricular pace pulse is typically programmed to be firstdelivered across the RV pace/sense electrodes 38 and 40, and an LVCDW^(P) is commenced. A left ventricular pace pulse is programmed to bedelivered to the LV CS pace/sense electrodes 48 and 50 if the LV CDW^(P)times out without the sensing of the R-wave at the LV-CS pace/senseelectrodes 48 and 50.

Then, the sequence is repeated such that if the V-A escape interval timeout, then an RA pace pulse is typically first delivered across the RApace/sense electrodes 17 and 19, the AV delay timer is restarted, andthe LA CDW^(P) time is commenced. An LA pace pulse is delivered to theLA CS pace/sense electrodes 28 and 30 if the LA CDW^(P) time times outwithout the sensing of the P-wave at the LA CS pace/sense electrodes 28and 30.

Each AV delay and CDW can be programmed to restore the normal activationsequence taking the particular conduction disturbance and the locationof the RA, LA, RV and LV pace/sense electrode locations into account.The activation sequence can also be modified to time these AV delays andCDWs from initial LA depolarizations arising from LA ectopic foci.

FIGS. 6 and 7 collectively are a simplified block diagram of acomprehensive, four channel IPG circuit of the present invention for theright and left heart chamber, four channel pacemaker IPG 14 employed inthe system of FIG. 5. FIG. 6 illustrates the RA and LA pacing andsensing circuitry 300 and 400, respectively in relation to thedata/control bus 122, the atrial pacer/timing logic circuit 120A, themicrocomputer components 108, 110, 112 and the programmable AV delaylogic 160. FIG. 7 illustrates the RV and LV pacing and sensing circuitry500 and 600, respectively in relation to the data/control bus 122, theventricular pacer/timing logic circuit 120V, the RF telemetrytransmitter/receiver 102 and the external programmer 90. Themicrocomputer components 108, 110, 112 and the atrial pacer/timing logiccircuit 120A of FIG. 6 are interconnected with the RV and LV pacing andsensing circuitry 500 and 600 and the ventricular pacer/timing logiccircuit 120V of FIG. 7 via the data/control bus 122. The RF telemetrytransmitter/receiver 102 of FIG. 7 is connected with the atrial pacertiming/logic circuit 120A of FIG. 6 via conductor 104, and theventricular pace trigger output signal from programmable AV delaycircuit 160 of FIG. 6 is coupled to the ventricular pacer/timing logiccircuit 120V of FIG. 7 via the conductor 162. The atrial and ventricularpacer/timing logic circuit 120A and 120V and the programmable AV delaycircuit 160 may alternatively be combined in a common circuit, as isconventional in DDD pacemakers.

The RA and LA pacing and sensing circuitry 300 and 400 and the RV and LVpacing and sensing circuitry 500 and 600 generally each follow thearchitecture of the RHC and LHC circuitry 100 and 200 of FIG. 4described above in detail. The blanking circuitry differs somewhat inthis four channel embodiment to allow for the blanking of all four ofthe RA, LA, RV and LV FDC sense amplifiers 326, 426, 526, 626 inresponse to delivery of a pace pulse by any of the RA, LA, RV and LVpace output circuits 334, 434, 534, 634. Each of the RA, LA, RV and LVprogrammable blanking circuits 336, 436, 536 and 636 generates a RA, LA,RV and LV BLANK signal on lines 318, 418, 518, and 618 having a durationprogrammed into RAM/ROM chip 110. The RA, LA, RV and LV BLANK signalsare triggered by atrial blanking (AB) and ventricular blanking (VB)trigger signals generated at the outputs of OR gate 314 and OR gate 514,respectively

The inputs of OR gate 314 are coupled with the outputs of OR gates 316and 416 which provide the RA and LA PACE signals delivered to the RA andLA pace output circuits 334 and 434, respectively. The OR gates 316 and416 pass the RA PT and LA PT signals selectively generated at theexpiration of the V-A escape interval and the programmable CDWs timed byprogrammable time delays 330 and 430.

Similarly, the inputs of OR gate 514 are coupled with the outputs of ORgates 516 and 616 which provide the RV and LV PACE signals delivered tothe RV and LV pace output circuits 534 and 634, respectively. The ORgates 516 and 616 pass the RV PT and LV PT signals selectively generatedat the expiration of the AV delay and the programmable CDWs timed by LVand RV CDW timers 530 and 630.

In operation, assume that the V-A escape interval is being timed outfrom a preceding ventricular sensed or paced event, and that aspontaneous atrial depolarization occurs in one of the RA or LA andfirst passes by one of the RA pace/sense electrode pair 17,19 or the LACS pace/sense electrode pair 28, 30 (FIG. 5). The SERA signal or theSELA signal is generated when the P-wave is sensed across the pace/senseelectrodes 17 and 19 or the LA CS pace/sense electrodes 28 and 30 by theRA FDC amplifier 326 or the LA FDC amplifier 426, respectively. Thefirst of the SERA or SELA signal to occur during the timing out of theV-A escape interval is employed to reset the current V-A atrial escapeinterval being timed out in the atrial pacer timing/logic circuit 120A.The first occurring SERA or SELA signal also starts the timing of therespective RA or LA CDW^(S) time by the respective RA or LA CDW timer330 or 430. The first occurring SERA or SELA signal is also applied toreset the LA or RA CDW timer 430 or 330, respectively, which would notbe timing out any CDW time under this circumstance. An atrial pace pulseis delivered to the other pair of atrial pace/sense electrodes by the RAor LA pacing output circuit 334 or 434 if the RA or LA CDW^(S) times outwithout the sensing of the P-wave at the other of the RA or LA CS atrialpace/sense electrodes 17 and 19 or 28 and 30.

Assuming that the V-A escape interval does time out without a P-wavebeing sensed, then either an RA pace pulse or a LA pace pulse isdelivered first by the respective RA pace output circuit 334 or LA paceoutput circuit 434, respectively, in response to the RA EI PT signal orthe LA EI PT signal, respectively. The selection of which atrial pacingpulse is delivered can be programmed. If the RA pace pulse is deliveredacross the RA pace/sense electrodes 17 and 19, and the LA CDW time iscommenced in LA CDW time timer 330. An atrial pace pulse is delivered tothe LA CS pace/sense electrodes 28 and 30 if the RA CDW time times outwithout the sensing of the P-wave at the LA CS pace/sense electrodes 28and 30.

In either case, the AV delay timer 160 is started to time out an AV timedelay on sensing of the P-wave or delivery of the atrial pace pulse. Asnoted above, preferably separate programmable paced AV delays that areemployed depending on whether the first atrial pacing pulsed isdelivered across the RA pace/sense electrodes 17 and 19 or the LA CSpace/sense electrodes 28 and 30. These separately programmable RSAV andLSAV delays and RPAV and LPAV delays are provided to take into accountthe particular locations of the RA and LA pace/sense electrodes and themeasured conduction time delays between those locations and thelocations of the RV and LV pace/sense electrodes. In FIG. 6, these fourpossible delays are programmed "ON" or "OFF" and the delay values areprogrammed into RAM/ROM chip 110. The programmed delay values are usedin the programmable AV delay timer 160 and started by one of the RSAV,LSAV trigger signals generated by the AV delay select logic or by one ofthe RPAV and LPAV trigger signals generated by the V-A escape intervaltimer(s) in atrial pacer timing/logic circuit 120A. Alternatively, onlya single RAV or LAV delay can be triggered in response to the RSAV andRPAV trigger signals or the LSAV and LPAV trigger signals, respectively.

In the most general case, if an R-wave is sensed across one pair of theRV or LV CS pace/sense electrodes 38 and 40 or 48 and 50 during the AVtime delay, the SERV or the SELV signal is generated by the RV FDCamplifier 526 or the LV FDC amplifier 626 and applied to reset logic inventricular pacer timing/logic circuit 120V. A reset signal is generatedon line 164 and employed to reset the AV delay timer 160 in FIG. 6. TheSERV or the SELV signal is also employed to start a V-A escape intervalin ventricular pacer timing/logic circuit 120V, and to start theventricular CDW time in the respective RV or LV CDW timer 530 or 630. Aventricular pace pulse is delivered to the other pair of ventricularpace/sense electrodes by the respective RV or LV pacing output pulsegenerator 534 or 634 if the ventricular CDW time times out without thesensing of the R-wave at the other pair of the RV or LV CS pace/senseelectrodes 38 and 40 or 48 and 50.

If the V-A escape interval times out, then the ventricular pace pulse istypically first delivered across the RV pace/sense electrodes 38 and 40,and the RV CDW time is commenced in RV CDW timer 530. A ventricular pacepulse is delivered to the LV CS pace/sense electrodes 48 and 50 by theLV pacing output circuit 634 if the ventricular CDW time times outwithout the sensing of the R-wave at the LV-CS pace/sense electrodes 48and 50.

Again, in respect to the RA and LA atrial sensing and pacing circuits300 and 400, the sensing characteristics of the RA and LA FDC amplifiers326 and 426, the CDW times of the CDW time timers 330 and 430 and thepacing pulse output circuits 334 and 434 can be separately programmedand stored in RAM/ROM chip 110. Similarly, in respect to the RV and LVsensing and pacing circuits 500 and 600, the sensing characteristics ofthe RV and LV FDC amplifiers 526 and 626, the CDW times of the CDWtimers 530 and 630 and the pacing pulse output circuits 534 and 634 canbe separately programmed and stored in RAM/ROM chip 110. Moreover,either or both of the bi-ventricular and bi-atrial operating modes canbe optionally programmed off to accommodate particular patients orchanges in a particular patient's condition. For example, it may bepossible to treat the above-referenced left atrial tachyarrhythmia byprogramming the above-described bi-atrial pacing mode on and selectingoptimum atrial conduction time delays and programming the bi-ventricularpacing and sensing functions off. Conversely, the bi-atrial pacing andsensing functions may be selectively programmed off, and thebi-ventricular pacing and sensing functions optimally programmed toprovide the proper therapy for a patient having normal interatrialconduction and abnormally long interventricular conduction delays.

FIG. 8 depicts a further simplified embodiment of a multi-channel pacingsystem 800 having A1 and A2 channels 802, 804 (which can be the RA andLA) and V1 and V2 channels 810, 812 (which can be the RV and LV). Forconvenience of illustration, blanking and refractory periods are notdepicted and the escape interval timing block is not depicted. Thedepicted four channel pacing system 800 can be programmed to operate ina single channel (i.e., in a single heart chamber), a two channel,bi-atrial or bi-ventricular, pacing system or in a three channel systemby disabling the un-used pacing channels and appropriate location of thepace/sense electrodes.

In a bi-atrial system comprising only atrial channels 802 and 804, itwill be assumed that an A--A escape interval is continuously being resetand timed out. Atrial P-waves that are sensed by either the A1 atrialsense amplifier 806 or A2 atrial sense amplifier 808 reset the A--Aescape interval and commence a Triggered CDWs in either the A1→A2 block830 or the A2→A1 block 826, respectively. Similarly, the delivery of anA1 or A2 pace pulse at the end of the A--A escape interval by the A1pace output 828 or the A2 pace output 832, respectively. resets the A--Aescape interval and commences a Triggered CDW^(P) in either the A1→A2block 830 or the A2→A1 block 826, respectively. The A2 pace output 832or the A1 pace output 828 is triggered at the end of the CDW^(S) or theCDW^(P) of block 830 or block 826, respectively, if the conducted atrialdepolarization is not sensed by A2 sense amplifier 808 or A1 senseamplifier 806 before the CDW^(S) or the CDW^(P) times out.

In a bi-ventricular system only comprising ventricular channels 810 and812, it will also be assumed that a V-V escape interval is continuouslybeing reset and timed out. Ventricular R-waves that are sensed by eitherthe V1 ventricular sense amplifier 814 or V2 ventricular sense amplifier820 reset the V-V escape interval and commence a Triggered CDW^(S) ineither the V1→V2 block 824 or the V2→V1 block 818. Similarly, thedelivery of V1 or V2 pace pulse at the end of the V-V escape interval bythe V1 pace output 816 or V2 pace output 822, respectively, resets theV--V escape interval and commences a Triggered CDW^(P) in either theV1→V2 block 824 or the V2→V1 block 818, respectively. The V2 pace output822 or the V1 pace output 816 is triggered at the end of the CDW^(S) orthe CDW^(P) if the conducted ventricular depolarization is not sensed byV2 sense amplifier 820 or V1 sense amplifier 814 before the CDW^(S) orthe CDW^(P) times out.

When all channels of the four channel system 800 are enabled, a V-Aescape interval is continuously being reset and timed out. It will beassumed that a V-A escape interval is timed from a selected V1 or V2paced or sensed event that is reset by a selected A1 or A2 paced orsensed event. A spontaneous, non-refractory R-wave occurring during thetime out of the V-A interval following a preceding ventricular sensed orpaced event that is sensed by the V1 or V2 sense amplifiers starts aV1→V2 Triggered CDW^(S) or a V2→V1 Triggered CDWs in blocks 824 and 818,respectively. Similarly, a spontaneous, non-refractory P-wave occurringduring the time out of the V-A interval following a precedingventricular sensed or paced event that is sensed by the A1 or A2 senseamplifiers starts an A1→A2 Triggered CDW^(S) or an A2→A1 Triggered CDWsin blocks 830 and 826, respectively.

In a four channel configuration of multi-channel pacing system 800, thesynchronized A→V pacing sequence following an A1 channel sensed or pacedevent can be selected to be A1→V1 or A1→V2. Similarly, the synchronizedA→V pacing sequence following an A2 channel sensed or paced event can beselected to be A2→V1 or A2→V2. The PAV^(A1) and SAV^(A1) delays arestarted in AV Delay block 838 to be timed out by an A1 pace output or anA1 sensed event, respectively. If the PAV^(A1) or SAV^(A1) delay timesout in block 838 without a V1 interrupt or V2 interrupt received fromthe V1 sense amplifier 814 or V2 sense amplifier 820, then either the V1pace output 816 or the V2 pace output 822 is triggered, depending on theprogrammed sequence. Then, the CDW^(P) in either the V2→V1 block 818 orV1→V2 block 824 is started to time out. The respective V1 pace output816 or V2 pace output 822 is triggered to produce the V1 pace pulse orthe V2 pace pulse unless a conducted R-wave is detected by the V1 senseamplifier 814 or the V2 sense amplifier 820 before the triggered CDW^(P)times out. A similar operation takes place if the V1 interrupt or V2interrupt is received from the V1 sense amplifier 814 or V2 senseamplifier 820 in response to a sensed R-wave. For example, the followingsensed and paced mode sequences are illustrated in FIG. 8 assuming theA1→V1 pacing sequence is selected and a sensed event occurs in atrialchannel 802:

    ______________________________________                                        SENSE MODE-Sensed event at A1 Sense Amplifier during V-A                      A1 Sense Inhibits A1 Pace Output                                              A1 Sense Triggers A1→A2 CDW.sup.s in 830                               A1 → A2 CDW.sup.s times out at programmed msec                         A1 → A2 CDW.sup.s time out triggers A2 Pace Output 832                 A1 → A2 CDW.sup.s time out triggers BLANK                              All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         A2 Pace Output delivers triggered pace pulse to Site                          A2                                                                            A1 Sense Triggers SAV.sup.A1 Delay in 838                                     SAV.sup.A1 times out at programmed msec and triggers V1 Pace                  Output 816                                                                    V1 Pace Out triggers BLANK                                                    All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         V1 Pace Output 816 delivers triggered pace pulse to Site                      V1                                                                            SAV.sup.A1 time out in 838 triggers V1 → V2 CDW.sup.s in block         836                                                                           V1 → V2 CDW.sup.s in block 836 times out at programmed msec            V1 → V2 CDW.sup.s time out triggers V2 Pace Output 822                 V1 → V2 CDW.sup.s time out triggers BLANK                              All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         V2 Pace Output 822 delivers V2 pace pulse to Site V2                          V1 - V2 CDW.sup.s interrupted by V2 Sense                                     V1 Sense Interrupts SAV.sup.A1 and Triggers V1→ V2 CDW.sup.s           in 836                                                                        V1 → V2 CDW.sup.s in block 836 times out at programmed msec            V1 → V2 CDW.sup.s time out triggers V2 Pace Output 822                 V1 → V2 CDW.sup.s time out triggers BLANK                              All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         V2 Pace Output 822 delivers V2 pace pulse to Site V2                          V1 → V2 CDW.sup.s interrupted by V2 Sense                              V-A escape interval times out                                                 A1 Pace Output delivers A1 pace to Site A1                                    A1 Pace Triggers A1 → A2 CDW.sup.s in 830                              A1 → A2 CDW.sup.s times out at programmed msec                         A1 → A2 CDW.sup.s time out triggers A2 pace Output 832                 A1 → A2 CDW.sup.s time out triggers BLANK                              All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         A2 Pace Output delivers triggered pace pulse to Site                          A2                                                                            A1 Pace Triggers PAV.sup.A1 Delay in 838                                      PAV.sup.A1 times out at programmed msec and triggers V1 Pace                  Output 816                                                                    V1 Pace Out triggers BLANK                                                    All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         V1 Pace Output 816 delivers triggered pace pulse to Site                      PAV.sup.A1 time out in 838 triggers V1 → V2 CDW.sup.s in block         836                                                                           V1 → V2 CDW.sup.s in block 836 times out at programmed msec            V1 → V2 CDW.sup.s time out triggers V2 Pace Output 822                 V1 → V2 CDW.sup.s time out triggers BLANK                              All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         V2 Pace Output 822 delivers V2 pace pulse to Site V2                          V1 → V2 CDW.sup.s interrupted by V2 Sense                              V1 Sense Interrupts PAV.sup.A1 and Triggers V1 → V2 CDW.sup.s in       836                                                                           V1 → V2 CDW.sup.s in block 836 times out at programmed msec            V1 → V2 CDW.sup.s time out triggers V2 Pace Output 822                 V1 → V2 CDW.sup.s time out triggers BLANK                              All Sense Amplifiers A1, A2, V1, V2 inhibited during                          BLANK                                                                         V2 Pace Output 822 delivers V2 pace pulse to Site V2                          V1 → V2 CDW.sup.s interrupted by V2 Sense                              ______________________________________                                    

In similar manner, all of the conceivable A1 and A2 pace and sense modesfor synchronous AV sequential pacing augmented with bi-atrial andbi-ventricular pacing can be practiced.

In any of these operating modes, the possibility exists that a pacingpulse will be delivered across the above-described right or left heartchamber pace/sense electrodes, and the delivered pacing pulse energywill appear across the other set of pace/sense electrodes masking theconducted P-wave or R-wave. This is particularly the case whenrelatively short CDW times are programmed to optimize timing of thesynchronous depolarization of the right and left heart chambers andconventional high gain sense amplifiers are employed. Thus, each senseamplifier for each pacing channel will require its own specificprogrammable blanking periods to avoid this problem and the problem ofsaturation of the sense amplifiers. For conventional, high gain senseamplifiers, the blanking periods are programmed in the range of 100msec. Much shorter blanking periods can be used with the FDC senseamplifiers. Refractory periods of the sense amplifiers are alsoprogrammable in the range of 20-350 msec for atrial channel senseamplifiers and 150-500 msec for ventricular channel sense amplifiers.During the refractory periods, sensed events will not be allowed toreset the pacing escape interval or AV delay being timed out.

The ability to sense a conducted evoked or spontaneous depolarization inone of the right or left heart chambers within a very short CDW from thepacing pulse or spontaneous depolarization to the other heart chamber isenhanced by use of FDC, right and left heart chamber, sense amplifiers.The FDC sense amplifier can be advantageously employed with conventionalcapacitive discharge pacing output circuits and short blanking periods.The blanking periods can be made even shorter using an FDC pacing outputcircuit which minimizes the pacing energy delivered and resulting afterpotentials on the delivery pace/sense electrodes. The use of the FDCcircuit also minimizes the energy of the pacing artifact at the otherpace/sense electrodes where the conducted evoked depolarization is to besensed. In addition, the use of the FDC sense amplifier coupled with thepace/sense electrodes allows the morphology of spontaneous and evokeddepolarizations conducted from a spontaneous or evoked depolarization inthe other chamber to be analyzed to determine pathologies of theconduction pathways.

A preferred sense amplifier circuit for use in the above-describedbi-chamber pacing systems as the FDC sense amplifier 126, 226, 326, 426,526, 626 is described in detail in the above-referenced U.S. Pat. No.5,902,324 and in commonly assigned U.S. Pat. Nos. 5,156,149, 5,233,985,and 5,370,665 by Hudrlik, which are incorporated by reference herein intheir entireties. The active circuitry of the FDC sense amplifiercircuit attempts to maintain an equilibrium condition between thepace/sense electrodes. The field perturbation caused by the passingcardiac depolarization or pacing artifact wavefront is nulled out by theactive circuitry which attempts to maintain a fixed relationship betweenthe potentials at the pace/sense electrodes coupled to the terminals. Indoing so, a very fast rise time, narrow voltage signal is generated thatcan be used in peak detection or threshold comparison to preciselyidentify the time of occurrence of the depolarization.

In the above preferred embodiments, it will be understood that the useof the FDC sense amplifier allows the programming of each CDW^(S) andCDW^(P) in a range of from 0 msec to any preferred upper limit. A sensedor paced event in one of the right or left heart chambers triggerssubstantially simultaneous delivery of a pacing pulse to the other heartchamber when the CDW^(P) and CDW^(S) is programmed at 0 msec. Themaximum programmable CDW^(S) and CDW^(P) is envisaged to be about 100msec to account for the physiologic activation sequence conductiondelays illustrated in FIG. 1. Or a long CDW can be programmed to allowsensing the conducted depolarization and measuring the actual pacetriggered or spontaneous conduction delay between any pair of right andleft heart chamber pace/sense electrodes. Or the long CDW can beprogrammed in cases where conduction between right and left heartchambers is absent to provide a highly delayed delivery of a pacingpulse following a sensed or paced event in one heart chamber to theother heart chamber to achieve a particular therapeutic timing ofdepolarizations of the right and left heart chambers.

Although bipolar atrial and/or ventricular lead systems are depicted inthe drawing figures and described above, it will be understood that thepresent invention may be employed with unipolar lead systems that employa single pace/sense electrode in the depicted positions in or about theright and left heart chambers and a remote electrode 20 formed as partof the outer surface of the housing of the IPG 12 in FIGS. 2, 3 and 5.Moreover other leads and pace/sense electrodes may be used instead ofthe depicted leads and pace/sense electrodes that are adapted to beplaced at electrode sites on or in the RA, LA, RV and LV.

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, therefore, that other expedientsknown to those of skill in the art or disclosed herein may be employed.In the following claims, means-plus-function clauses are intended tocover the structures described herein as performing the recited functionand not only structural equivalents but also equivalent structures. Forexample, although a nail and a screw may not be structural equivalentsin that a nail employs a cylindrical surface to secure wooden partstogether, whereas a screw employs a helical surface, in the environmentof fastening wooden parts, a nail and a screw are equivalent structures.

It is therefore to be understood, that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed without actually departing from the spirit and scope of thepresent invention.

What is claimed is:
 1. A pacing system for improving the hemodynamicefficiency of a sick heart suffering from conduction delays inconducting spontaneous or evoked depolarizations originating in one ofthe right or left ventricle to the other of the left or right ventriclecomprising:right ventricular lead means for locating first and secondright ventricular pace/sense electrodes in relation with the rightventricle; left ventricular lead means for locating first and secondleft ventricular pace/sense electrodes in relation with the leftventricle; right ventricular depolarization sensing means coupled withsaid right ventricular lead means for sensing spontaneous cardiacdepolarizations originating in the right ventricle and conducted cardiacdepolarizations originating in the left ventricular from a spontaneouscardiac depolarization or delivery of a left ventricular pacing pulse tothe left ventricle and for providing a right ventricular sensed eventsignal in response to either a sensed spontaneous or conducted cardiacdepolarization; left ventricular depolarization sensing means coupledwith said left ventricular lead means for sensing spontaneous cardiacdepolarizations originating in the left ventricle and conducted cardiacdepolarizations originating in the right ventricular from a spontaneouscardiac depolarization or delivery of a right ventricular pacing pulseto the right ventricle and for providing a left ventricular sensed eventsignal in response to either a sensed spontaneous or conducted cardiacdepolarization; escape interval timing means for timing an escapeinterval establishing a pacing rate and providing an escape intervalpace trigger signal at the time out of the escape interval, the escapeinterval timing means further comprising reset means for restarting thetiming of the escape interval in response to one of the right or leftventricular sensed event signals; right ventricular pacing pulse outputmeans coupled with said right ventricular lead means and selectivelyresponsive to an applied pace trigger signal for generating anddelivering a right ventricular pacing pulse to said right ventricularlead means to evoke a right ventricular depolarization; left ventricularpacing pulse output means coupled with said left ventricular lead meansand selectively responsive to an applied pace trigger signal forgenerating and delivering a left ventricular pacing pulse to said leftventricular lead means to evoke a left ventricular depolarization; meansfor applying said escape interval pace trigger signal to one of saidright ventricular pacing pulse output means or said left ventricularpacing pulse output means; left ventricular conduction delay windowtiming means coupled with said escape interval timing means and saidright ventricular depolarization sensing means for timing a leftventricular conduction delay window from a right ventricular sensedevent signal and selectively from an escape interval pace trigger signaland for providing a left ventricular pace trigger signal at theexpiration of the left ventricular conduction delay window time, saidleft ventricular conduction delay window timing means further coupledwith said left ventricular depolarization sensing means and comprisingleft ventricular window terminating means for terminating the timing outof the left ventricular conduction delay window in response to a leftventricular sensed event signal; means for applying said leftventricular pace trigger signal to said left ventricular pacing pulseoutput means as a pace trigger signal for triggering the generation anddelivery of a left ventricular pacing pulse to said left ventricularlead means; right ventricular conduction delay window timing meanscoupled with said escape interval timing means and said left ventriculardepolarization sensing means for timing a right ventricular conductiondelay window from a left ventricular sensed event signal and selectivelyfrom an escape interval pace trigger signal and for providing a rightventricular pace trigger signal at the expiration of the rightventricular conduction delay window time, said right ventricularconduction delay window timing means further coupled with said rightventricular depolarization sensing means and comprising rightventricular window terminating means for terminating the timing out ofthe right ventricular conduction delay window in response to a rightventricular sensed event signal; and means for applying said rightventricular pace trigger signal to said right ventricular pacing pulseoutput means as a pace trigger signal for triggering the generation anddelivery of a right ventricular pacing pulse to said right ventricularlead means; whereby an excessive conduction delay between a spontaneousor evoked depolarization in the right ventricle and the conducteddepolarization wave in the left ventricular or an excessive conductiondelay between a spontaneous or evoked depolarization in the leftventricle and the conducted depolarization wave in the right ventricleis corrected by generation and delivery of a pacing pulse to the left orright ventricle, respectively at the timing out of the correspondingconduction delay window.
 2. The pacing system of claim 1, furthercomprising means for programming said left ventricular conduction delaywindow in a range of 0-100 msec.
 3. The pacing system of claim 1,further comprising means for programming said right ventricularconduction delay window in a range of 0-100 msec.
 4. The pacing systemof claim 1, further comprising:means for preventing the sensing ofspontaneous and evoked cardiac depolarizations in the right ventricleand the provision of a right ventricular sensed event signal in responsethereto for the duration of a right ventricular blanking period inresponse to the generation of a ventricular pacing pulse; and means forpreventing the sensing of spontaneous and evoked cardiac depolarizationsin the left ventricle and the provision of a left ventricular sensedevent signal in response thereto for the duration of a left ventricularblanking period in response to the generation of a ventricular pacingpulse.
 5. The pacing system of claim 4, further comprising means forprogramming said left ventricular conduction delay window in a range of0-100 msec.
 6. The pacing system of claim 4, further comprising meansfor programming said right ventricular conduction delay window in arange of 0-100 msec.
 7. A pacing method for improving the hemodynamicefficiency of a sick heart suffering from conduction delays inconducting spontaneous or evoked depolarizations originating in one ofthe right or left ventricle to the other of the left or right ventriclecomprising the steps of:locating first and second right ventricularpace/sense electrode in relation with the right ventricle; locatingfirst and second left ventricular pace/sense electrodes in relation withthe left ventricle; sensing spontaneous and evoked cardiacdepolarizations in the right ventricle across said right ventricularpace/sense electrodes and providing a right ventricular sensed eventsignal; sensing spontaneous and evoked cardiac depolarizations in theleft ventricle across said left ventricular pace/sense electrodes andproviding a left ventricular sensed event signal; timing an escapeinterval establishing a pacing rate and providing an escape intervalpace trigger signal at the time out of the escape interval; restartingthe timing of the escape interval in response to one of the right orleft ventricular sensed event signals; in response to the escapeinterval pace trigger signal, selectively triggering either rightventricular pacing pulse output means coupled with said rightventricular pace/sense electrodes to generate and deliver a rightventricular pacing pulse to said right ventricular pace/sense electrodesto evoke a right ventricular depolarization or left ventricular pacingpulse output means coupled with said left ventricular pace/senseelectrodes to generate and deliver a left ventricular pacing pulse tosaid left ventricular lead means to evoke a left ventriculardepolarization; timing a left ventricular conduction delay window from aright ventricular sensed event signal or from generation of a rightventricular pacing pulse and providing a left ventricular pace triggersignal at the expiration of the left ventricular conduction delay windowterminating the timing out of the left ventricular conduction delaywindow in response to a left ventricular sensed event signal; applyingsaid left ventricular pace trigger signal to said left ventricularpacing pulse output means to trigger the generation and delivery of aleft ventricular pacing pulse to said left ventricular lead means;timing a right ventricular conduction delay window from a leftventricular sensed event signal or from generation of a left ventricularpacing pulse and providing a right ventricular pace trigger signal atthe expiration of the right ventricular conduction delay windowterminating the timing out of the right ventricular conduction delaywindow in response to a right ventricular sensed event signal; andapplying said right ventricular pace trigger signal to said rightventricular pacing pulse output means to trigger the generation anddelivery of a right ventricular pacing pulse to said right ventricularlead means; whereby an excessive conduction delay between a spontaneousor evoked depolarization in one of the right or left ventricle and theconducted depolarization wave in the other of the left or rightventricle is corrected by generation and delivery of a pacing pulse atthe timing out of the conduction delay window.
 8. The pacing method ofclaim 7, further comprising the steps of:programming said leftventricular conduction delay window in a range of 0-100 msec; andprogramming said right ventricular conduction delay window in a range of0-100 msec.
 9. The pacing method of claim 7, further comprising thesteps of:preventing the sensing of spontaneous and evoked cardiacdepolarizations in the right ventricle and the provision of a rightventricular sensed event signal in response thereto for the duration ofa right ventricular blanking period in response to the generation of aventricular pacing pulse; and preventing the sensing of spontaneous andevoked cardiac depolarizations in the left ventricle and the provisionof a left ventricular sensed event signal in response thereto for theduration of a left ventricular blanking period in response to thegeneration of a ventricular pacing pulse.
 10. The pacing method of claim9, further comprising the steps of:programming said left ventricularconduction delay window in a range of 0-100 msec; and programming saidright ventricular conduction delay window in a range of 0-100 msec. 11.A pacing method for improving the hemodynamic efficiency of a sick heartsuffering from conduction delays in conducting spontaneous or evokeddepolarizations originating in the right ventricle to the left ventriclecomprising the steps of:locating first and second right ventricularpace/sense electrode in relation with the right ventricle; locatingfirst and second left ventricular pace/sense electrodes in relation withthe left ventricle; sensing spontaneous and evoked cardiacdepolarizations in the right ventricle across said right ventricularpace/sense electrodes and providing a right ventricular sensed eventsignal; sensing spontaneous and evoked cardiac depolarizations in theleft ventricle across said left ventricular pace/sense electrodes andproviding a left ventricular sensed event signal; timing an escapeinterval establishing a pacing rate and providing an escape intervalpace trigger signal at the time out of the escape interval; restartingthe timing of the escape interval in response to the right ventricularsensed event signals; in response to the escape interval pace triggersignal, triggering the right ventricular pacing pulse output meanscoupled with said right ventricular pace/sense electrodes to generateand deliver a right ventricular pacing pulse to said right ventricularpace/sense electrodes to evoke a right ventricular depolarization;timing a left ventricular conduction delay window from a rightventricular sensed event signal or from generation of a rightventricular pacing pulse and providing a left ventricular pace triggersignal at the expiration of the left ventricular conduction delay windowterminating the timing out of the left ventricular conduction delaywindow in response to a left ventricular sensed event signal; andapplying said left ventricular pace trigger signal to said leftventricular pacing pulse output means to trigger the generation anddelivery of a left ventricular pacing pulse to said left ventricularlead means; whereby an excessive conduction delay between a spontaneousor evoked depolarization in the right ventricle and the conducteddepolarization wave in the left ventricle is corrected by generation anddelivery of a pacing pulse at the timing out of the conduction delaywindow.
 12. The pacing method of claim 11, further comprising the stepof:programming said left ventricular conduction delay window in a rangeof 0-100 msec.
 13. The pacing method of claim 11, further comprising thesteps of:preventing the sensing of spontaneous and evoked cardiacdepolarizations in the right ventricle and the provision of a rightventricular sensed event signal in response thereto for the duration ofa right ventricular blanking period in response to the generation of aventricular pacing pulse; and preventing the sensing of spontaneous andevoked cardiac depolarizations in the left ventricle and the provisionof a left ventricular sensed event signal in response thereto for theduration of a left ventricular blanking period in response to thegeneration of a ventricular pacing pulse.
 14. The pacing method of claim13, further comprising the step of:programming said left ventricularconduction delay window in a range of 0-100 msec.
 15. A pacing systemfor improving the hemodynamic efficiency of a sick heart suffering fromconduction delays in conducting spontaneous or evoked depolarizationsoriginating in the right ventricle to the left ventriclecomprising:right ventricular lead means for locating first and secondright ventricular pace/sense electrode in relation with the rightventricle; left ventricular lead means for locating first and secondleft ventricular pace/sense electrodes in relation with the leftventricle; right heart sensing means for sensing spontaneous and evokedcardiac depolarizations in the right ventricle across said rightventricular pace/sense electrodes and providing a right ventricularsensed event signal; left heart sensing means for sensing spontaneousand evoked cardiac depolarizations in the left ventricle across saidleft ventricular pace/sense electrodes and providing a left ventricularsensed event signal; escape interval timing means for timing an escapeinterval establishing a pacing rate and providing an escape intervalpace trigger signal at the time out of the escape interval; reset meansfor restarting the timing of the escape interval in response to theright ventricular sensed event signals; right ventricular pacing pulseoutput means coupled with said right ventricular pace/sense electrodesresponsive to the escape interval pace trigger signal for generating anddelivering a right ventricular pacing pulse to said right ventricularpace/sense electrodes to evoke a right ventricular depolarization; meansfor timing a left ventricular conduction delay window from a rightventricular sensed event signal or from generation of a rightventricular pacing pulse and providing a left ventricular pace triggersignal at the expiration of the left ventricular conduction delay windowmeans for terminating the timing out of the left ventricular conductiondelay window in response to a left ventricular sensed event signal; andleft ventricular pacing pulse output means coupled with said leftventricular pace/sense electrodes and responsive to said leftventricular pace trigger signal for generating and delivering a leftventricular pacing pulse to said left ventricular lead means; whereby anexcessive conduction delay between a spontaneous or evokeddepolarization in the right ventricle and the conducted depolarizationwave in the left ventricle is corrected by generation and delivery of apacing pulse at the timing out of the conduction delay window.
 16. Thepacing system of claim 15, further comprising means for programming saidleft ventricular conduction delay window in a range of 0-100 msec. 17.The pacing system of claim 15, further comprising:means for preventingthe sensing of spontaneous and evoked cardiac depolarizations in theright ventricle and the provision of a right ventricular sensed eventsignal in response thereto for the duration of a right ventricularblanking period in response to the generation of a ventricular pacingpulse; and means for preventing the sensing of spontaneous and evokedcardiac depolarizations in the left ventricle and the provision of aleft ventricular sensed event signal in response thereto for theduration of a left ventricular blanking period in response to thegeneration of a ventricular pacing pulse.
 18. The pacing system of claim17, further comprising means for programming said left ventricularconduction delay window in a range of 0-100 msec.